Before committing to building the frames I first obtained the necessary sheets
of 6mm MDF for the top (I can hear all the plywood-advocates cringing from
here). This was cut into 3'x2' rectangles by the
DIY store for no better reason than it made it easier to take home
in the
car! The bare
sheets were used for rough setting out - on the lounge carpet - making
use of Peco point templates. You may notice that at this point the
branchline met the mainline at a flat junction. I knew I wanted the
station to be a certain length, and
the fiddle
yard
to
be wide enough for 8 storage tracks, so these were drawn on seperate
pieces of cardboard so they could be moved around for the best positioning.

Outside
frames were built out of 3"x2" softwood glued-and-screwed,
ensuring they remained square until dry. Cross beams and bracing were then
installed, also glued-and-screwed, made out of 2" x ¾" timber
in a T-shape as per the diagram below, with holes pre-drilled in the upright
pieces to allow routing for wires. This should ensure a high degree of rigidity
to minimise flexing while the layout is being transported and during set
up.

This may seem to be on the heavyweight side but since it was decided from
the start that a van would be hired to transport it, and two people would
be needed to operate it and therefore be available to set it up, I would
rather over-engineer at this stage than deal with damage due to flexing when
all the scenics are down! So having built the frames the MDF sheets were
firmly screwed in place, making a VERY solid baseboard. Believe me it does
not flex ;o)

A closer view underneath showing the T-braces and the wiring holes.

With both boards built attention turned to finalising the track-plan,
mostly freehand with a marker and ruler but again using Peco templates
for the points. Done in the garden as there is nowhere in the house
to
have both boards up for any length of time.

Here
you can see the early planning of the flat junction for the branch
on the far board, now superceded by the over-bridge idea, the beginnings
of which are on the nearer board. The large blank rectangle in the foreground
is where the cardboard template for the station sits.

To
ensure good alignment between the two boards they were placed on edge
on the flat wooden floor in the lounge and two 7.5mm holes were
drilled right through one end frame approximately 4" from
the ends and 1½" apart as shown below. Then the two boards
were clamped together making sure the top surfaces were level with each
other
and
the same holes extended 8mm into the adjoining frame. At the same
time a
further
9.5mm hole was drilled right through 10" from each end to provide
bolt holes later. The boards were
separated and 8mm Bullet-type Alignment Dowels from Station
Road Baseboards fitted - the female halves glued and gently tapped
into the blind holes, and the male parts glued and tapped into the through-holes.
To reinforce the latter some 8mm dowel rod was glued and hammered into
the hole from behind until they butted against the back of the male dowels.
Measurement diagram below:-

Female
dowels fitted into 7.5mm dia by 8mm deep blind holes

Male
half of dowels fitted into 7.5mm holes drilled right through

Wooden
dowels glued and hammered in to reinforce male dowels from the rear

M8
T-Nuts, again from Station Road Baseboards, were fitted into the two
9.5mm holes of one board on the opposite side to the join, and
drilled T-Nuts fitted to the other board. Some M8 threaded rod was cut
to
length to fit through both end-timbers and a wingnut glued on each one
with
Araldite. The idea when assembling the layout is that
the two boards are placed on the modified trestles and slid together
so the alignment dowels engage. The two threaded bolts are pushed
through the drilled T-Nuts and both end-timbers and screw into the threaded
T-Nut
on the other side, bringing the two boards tightly together.